The following items were discussed at the Signal Class on May 3, 2003:
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| Track Circuit Experiments: |
Set up and experimented with DC, AC, Style 'C', and AC-Relay-Replace Track Circuits.
Also experimented with the US&S ATT20 audio track circuit unit.
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| Track Circuit Install Fundamentals: |
- The following is the normal sequence of steps for setting up a new track circuit:
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- Setup voltage source to approx twice track relay pickup voltage (typically 0.5 volt for DC circuit).
This will need to be a multiple of 1.25 VDC (nicad) or 2.20 (lead-acid) if battery backup will be used.
- Adjust track resistor to 1 ohm.
- Test track with a 0.06 ohm test shunt (equivalent to 14.7 ft of #14 wire) and verify circuit drops.
- If circuit doesn't drop, add resistance until circuit drops with 0.06 ohm shunt test.
- Retest track at each end and center of block and adjust resistor as needed.
- In general, the above is applicable to all types of track circuits.
NOTES:
For calculation rule of thumb assume "normal" ballast is 4 ohms per 1000 feet.
Typically use 0.5 ohm track relay for track circuits >5000 feet,
and a 4 ohm track relay for track circuits <5000 feet.
Style-C circuit is usually only good for <1000 feet track circuits.
A DC track relay will NOT pick up at ANY AC voltage.
Do NOT radically adjust an existing track circuit without understanding why these big changes are needed --
otherwise you may be compensating for broken equipment, broken rails or some other
aberational condition which should be corrected.
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